The use of artificial heart valves is well known in the art. The valves are typically supported in suture rings that are sewn to the surrounding tissues of the heart. Commonly used valves of the bileaflet type are disclosed in U.S. Pat. Nos. 4,254,508, 4,276,658, and 4,328,592. Such valves include two leaflets pivotally mounted within an orifice ring which is a conduit for blood. The leaflets pivot between an open position to allow blood to flow, and a closed position to prevent blood flow. The valve bodies, sometimes referred to as orifice rings, are typically formed of resilient materials, such as graphite, pyrocarbon, or pyrocarbon-coated graphite, and are typically designed to be deformed sufficiently to provide room to insert the leaflets, but which will return to an unstressed, annular configuration.
It is desirable to provide a structure for increasing the stiffness of the orifice ring after the leaflets are installed. Such structure is generally a stiffener ring mounted to the exterior of the orifice ring. The stiffener ring is held within a shallow annular groove formed in the outer circumferential surface of the orifice ring by an interference fit. The combination of the stiffener ring and the orifice ring provides greatly increased stiffness and resistance to deformation, compared to that of the orifice ring alone. Stiffener rings also provide an attachment site for affixing the suture ring to the valve. Another function of the stiffener ring is to provide a structure that resists forces that may be generated during implantation of the valve into the heart that could possibly damage the orifice ring, or damage or dislodge one of the leaflets.
U.S. Pat. No. 4,535,483 discloses a suture ring (hereinafter the '483 suture ring) which is designed to be mounted to a bileaflet valve of the type described above. The suture ring includes a stiffener ring which is seated and held within a groove formed in the outer circumferential surface of the orifice ring by an interference fit. The outer circumferential surface of the stiffener ring extends beyond the outer diameter of the orifice ring and provides an attachment site for the suture ring. The '483 suture ring includes a retainer ring having an inner annular groove and a ring of curved tines extending radially from one end of the retainer. The opposite side of the retainer ring has a ring of tangs with lugs extending radially inward towards the center of the ring. A resilient polymeric filler ring fits around the ring of tines and is held in place by a fabric material wrapped completely around the retainer ring, filler ring, and lugs. The fabric material, selected to be compatible with blood and heart tissue, is tied around the retainer ring with sutures. The assemblage of the retainer ring, filler ring, and fabric is mounted to the valve by pressing the retainer ring over the stiffener ring so that the lower surfaces of the lugs outwardly cam when they contact the upper edges of the stiffener ring. As the lugs cam outwardly, the tangs resiliently deform outwardly. When the flat upper surfaces of the lugs reach the bottom of the stiffener ring, the tangs spring back inwardly. At this stage, the stiffener ring is captured within the inner annular groove of the retainer ring whereby the retainer ring is secured to the orifice ring.
Although the '483 suture ring is an adequate design, if the retainer ring could be eliminated, there would be additional space for an orifice ring structure in the space normally occupied by the retainer ring so an orifice ring having a larger inside diameter could be used. Such an orifice ring could have a larger orifice flow area, and hence, relatively low fluid flow resistance. An orifice having low flow resistance would provide increased blood flow, a desirable characteristic in a mechanical heart valve.
U.S. Pat. No. 3,996,623, discloses a type of suture ring that is sewn to a heart valve with stitches. During implantation of a such a suture ring, the stitches holding the suture ring to the heart valve are vulnerable to inadvertently being cut by the surgeon, possibly causing the sewing ring to become separated from the heart valve. Therefore, there is a need for a suture ring that may be attached to a heart valve in a manner which is less susceptible to being damaged or cut.
There is also a need for a suture ring that does not require a retainer ring in order to accommodate an orifice ring having an overall larger orifice area than present orifice rings. A further need exists for a suture ring which supports a heart valve prosthesis where the valve may be rotated with relatively little torque to enable a surgeon to easily position the valve at the implantation site without risk of damaging the valve or the heart tissue.